Liquid oxygen converter apparatus



Nbv. 3, 1953 v w. A. WILDHACK LIQUID OXYGEN CONVERTER APPARATUS Original Filed Feb. 5, 1946 JNVENTOR. WILLIAM A. WILDHAGK ATTORNEY Patented Nov. 3, 1 953 LIQUID OXYGEN CONVERTER APPARATUS William A. Wildhack, Arlington, Va.

Original application February 5, 1946, Serial No.

645,692, now Patent N 0. 2,576,985, dated Decem- -ber 4, 1951. Divided and this application tober 10, 1951, Serial No. 250,777

(Granted under Title 3-5, U. S. "Code (1952),

6 Claims.

This invention relates to liquid oxygen converters, and more particularly to such converters adaptable for use in aeronautics for oxygen supply to personnel at high altitudes, for charging oxygen containers for such supply, and other similar purposes wherever controlled quantities of liquid oxygen might be desired to be transferred either as a liquid, or converted and transferred in gaseous form most economically.

The main object of the present invention is to provide apparatus for handling liquid oxygen safely and economically and to construct means for transferring it either as liquid or converting it into gaseous form and transferring it to supply or storage containers or directly to the point of use, such as breathing masks, or for internal combustion engine or rocket feeding, etc.

A further object is to construct apparatus in connection with a liquid oxygen container for converting and delivering the oxygen in gaseous form at any required rate to a supply line in a most economical manner by simple and quickly responsive means.

Other and more specific objects will appear in the following detailed description of an embodiment of this invention, having reference to the accompanying drawings, wherein:

Fig. 1 is a view of apparatus illustrating the principle of operation;

Fig. 2 is a view of the specific arrangement of the claimed apparatus; and

Fig. 3 is a sectional view of an adjustable pressure-closing valve insertible in the pressure line of the apparatus.

Principle of operation In the closed circulation system for pressure build-up, characteristic of these converters, liquid flowin by gravity from the bottom of the charge is evaporated by atmospheric heat at a level lower than that of the surface of the liquid in the container; the resulting gas continues through the warming coil and is forced by the pressure of the liquid column into the space above the liquid. or back in o he liquid at a higher level. This gas condenses, warming the liquid with which it comes in contact and forming a heated layer, at the liquid surface, of higher vapor pressure. The pressure increase is the same in the liquid phase as in the gaseous phase, so that the circulation, which depends only on a difierential pressure due to the height of the liquid column above the evaporator, continues the process until stopped by a pressure-operated valve, or, in an ultra high-pressure system, until the density of the warm gas at the high pressure approaches that of the liquid.

Since the density of liquid oxygen decreases rapidly with increasing temperature, the heated liquid tends to rise or to stay on the surface. Thus it is easily possible to obtain a high pressure over the liquid quickly by supplying to the by atmospheric evaporating coils in the models to be described, it will be apparent that the same principle of operation could be employed with electric or flame heating.

Description of converter The schematic diagram of model I is shown in Fig. 1. Besides the container I, filling and withdrawal means 2, relief valve 3, and pressure gage 4, there are four rather independent flow or pressure circuits which are parts of the total converter assembly: the pressure build-up circuit, the supply circuit, an optional economizing circuit, and the contents measuring circuit. The container, as illustrated, has an upper section which normally contains the gas and a lower section which normally contains the liquid, these sections being also referred to as gas phase and liquid phase sections.

Pressure build-up circuit.-The container I having a vacuum jacket 46 is provided with a bottom connection which has a gooseneck 5 or other liquid trap. Attached to this is an evaporating and warming coil 6 (pressure build-up evaporator) which is connected to the vapor phase 1 above the liquid 8 through a pressure evaporator is acted upon at one-end -byfih epres: sure of the liquid, at the other; end bythepries: sure of the gaseous phase. Themressurediers ence is just that of the column of liquid;- Ifno evaporation occurred, the liquid would then flow.

through the pressure evaporator until it "stood at the same level inside the container-and in the: Because of evaporation in the? tube outside. pressure evaporator coilv an unbalance of pressure, occurs and persists and causes a continuing circulation; forcin gasinto; the space 7 above the liquid and increasing the pressure by; QUIT}:- pression. This; pressure is transmitted through the liquid, so that the pressure at the bottom of the liquid increases at the same rate as that abbveit. r The rateof increase of pressure would bellmited only by the rate at which the inflow of gas dueto the circulation would increase the pressure in the volumeabovethe liquid, were, it not for a retardation of the process occasioned b'yjth'e condensation of the gas on the top of the liquid. However, the heat of condensation :tends to warm the top layer of the liquid 8 so that a layer H of warmed liquid is formed, in which there is a steep temperature gradient Because of the lower density of warm liquid this warm layer'is in strong gravitationalequil'brium, and persists for some time even whennioderate shaking o cru -l When the ssure ha in reas to h desired value, they pressure operated valve} closes, stopping the circul tion Withou t this control, the pressure would continue; toincrease indefinitely unless the manual valve IU were againclosed. p M, d I

The rate of increase of pressure isa function f t e pressure. f. i 1l 1.,h a h iq e r the e ra warmin wil th rei t n e o ow n the i eu etm c r uitth lum li h se. t gereaoi he liquid surface. In practice, the pressure has been raised from atmospheric tq 9 p s iginfrog n i one to minutes, the longer time being required in a model in' which there" was a considerable restriction to flow in the connection to" the drain tube. From 2 to 5 minutes appears to be a'reasonably attainable performance for service models. If a cylindrical container were used, an insulating float covering most of the liquid surface might aid in reducing the amount of gas to bercondensed andreduce the time required.

Supply circuit-When a flow of oxygen is required in the delivery line 1,2; the supply connection 43 is opened and the decrease of pressure in the line allows liquid to be forced up the tube 13 and into the main evaporatingcoil I4, where it evaporates and is warmed; The temperature differential between the delivered gas and the ambient air is, of course; dependent on the size andeiiiciency of the warming coil; which must bedesigned to meet the requirements for the particular application:

The maximum continuous flow which can be evaporated and warmed to within 0 C, f amdown by the liquid desired, the manual valve Hi is opened. The gas in the pressurebuild-up= 'liquid and thus prevent bient temperature is a reasonable criterion of the performance required for aircraft use. In various models, rates from 20 to 200 liters per minute at standard temperature and pressure (1. p. m., s? t. pl); lravbeen ob'teliifti? For tlie highest rate a coil of feet of '%'-inchl. D. dural tubin was used.

The pressure drop across the warming coil must-beconeiderecl;particularly since it is desirable; to providefo'r'peak flow rates considerably larger than th e continuous rating. A tube of relatively large diameter is thus preferred, especiall'i's'inceHt principle, about the only lirn ation onthiinstantaneous flows available.

E onomizmg-;circuii.-When the whole mass of liquid has been warmed to a temperature correspending to the working pressure, or above, it maybe-desirable to draw gas from above the loss of gas through the pressure relief valve 3-. This may be done by a pressureopening valve l 5, connected as shown in rest 1, which opens'a'ta pressure somewhat above ca amaran the pressure-closing valve 9 'closes.

During'"delivery, then, gaswiil be drawn from the vapor phase above the liquid through tube It,'prssiire'opening valve i5 and coil l4 until the evaporation has cooled the remaining liquid and reduced the vapor pressure sufficiently for tli'p're'ssure opening valve' 5 5 to'close again.

Whennot'delivering, the opening of the pressure-opening valve has" no effect; the pressure continues tdris'slowly, at a rate determined by the amount" of liquid and the degree of insulation o'f'the container, until the pressure relief valves begins to leak. Gas will then escape at a' r'at'e determined by the heat flow into the liquid. K a I Ifused under conditions of frequent intermitt'ent' delivery, it may" be" desirable to provide a check valve I'I betweenthe pressure-opening valve'flland the delivery line l2, as shown in Fig'. 1; to'prevent oVe'r p-ressure being developed by" evaporation of residual liquid in the evaporator forcing gas into the spac'eab'ove the liquid after delivery has stopped, with resultant loss throughjthe relief valve. The excess gas would then bubble back thrioughl the liquid and condense, at least partially. The provision of a ballast'tank, or receiver, in th'e'supply circuit would also be effective in reducing such losses.

Contemts indicationieThe amount of liquid remaining in the containerriiay be determined by the'jdifference in pressure between the gas phase and th bOttbhI Outlet.

A differential pressure gage it of a range 0' to lOor ZOinChe's'of water c'of'rine'ct'e d asshown is suitableffor this purposel The differential pressure" isy of' course, not'proportionalto content for a sphe'r'ical container, and the g'age'must be designed or calibrated accordingly.

The lines' lfl" andZc to the gage may be of very sirnall, light tubing, and} may extend to a considerable distance, providing for remote indication.

The conditions of use here require that the case of the gage should beable to withstand a pressuregreater than the normal delivery pressi 'r. Such gages are not readily available commercia'uy'.

Several small mercury inanometers, fitted with sintered glass stoppers, have been used successfully The mechanis'r'n from an aircraft fuelquantity gage can be used when placed in a suitably strong case, but the size, weight, and the thickness of th cover glass required are objectionable features. Suitable gages have been -made along these lines.

Filling-Provision is made in the model shown for filling at either the top through a vent or filling valve 2|, or the bottom of the container, and

for withdrawal at the bottom. For convenience in filling or withdrawal, a quickly detachable connector is desirable. This connector must function at liquid air temperature, and should be suitably protected so that frost does not get portable converters or for aircraft converters;

since both the bulk and weight of the apparatus can be substantially reduced. In designing the single evaporator 2'8, it is necessary that under normal delivery rates the liquid'level be lower in the coil than in the container by an amount greater than the pressure drop in the coil for that delivery rate. This maintains the flow in a direction so that an adequate gas phase pressure at the container is maintained when the pressure-closing valve 9 is open. Abnormally high delivery rates may be obtained intermittently, the pressure building up to normal during periods of lower delivery. A lightly loaded check valve 24 may be included in the pressure circuit to ensure that gas is not withdrawn from the gas phase during such periods when the pressure happens to be below normal.

Forthis arrangement, also, a pressure-opening valve l5 may be added to permit withdrawal from the gas phase when the pressure is above normal, as shown in Fig. 2. With this, however,

a loaded check valve 23 is also required to ensure that the pressure at the pressure-opening valve and the pressure in the delivery line, is less than that in the gaseous phase in the container. Without this, there would be the possibility of circulation through the pressure-opening valve, causing the pressure to build up still higher.

Fig. 2.

Charging converter As a converter of oxygen, the applications of the device so far described would presumably be mainly in supplying breathing oxygen in hospitals and in aircraft, and supplying welding and burning oxygen .in industry. Another application which may be of some importance is in charging high pressure cylinders with gas. For

. this use, the converter must be structurally able .to withstand the charging pressure.

This requires a special container, but otherwise nothing other than conventional design.

It has been mentioned that the limiting pressure possible of theoretical attainment by the circulation-pressure method is that at which the density of the gas in the other coil, at the coil temperature, approaches the density of the liquid. If the liquid were originally in equilibrium with atmospheric pressure, its density would be about 1.1 g./cc. Gas at room temperatures would have to be at a pressure of nearly 10,000 p. s. i. to equal this density. It appears theoretically possible, therefore, to obtain very high pres- The best location for this check valve is as shown in sures by this method. The limit has not been investigated because of the lack of suitable containers, but a pressure of 3000 p. s. i. was obtained easily.

Any of the methods known in the art of heat interchanger design could be used to increase the conversion rate. Several coils could'be used in parallel, if desired, or the evaporator could be surrounded by water, ventilated by a forced draft, or heated by a flame or electric heater. In charging cylinders, a high conversion rate is desirable, but there is no need for the delivered gas to be warmed very near the ambient temperature.

Since the rate of delivery may be excessive in charging a cylinder at low pressure, if no limitation is provided when the charging valve is opened, it will be desirable to install a flow regulator or flow indicator. A differential pressure gage across a restriction is a simple method of indication, if suitably strong difierential gages are available. A pressure-opening valve, installed near the charging valve, would serve as a flow regulator if the restriction to flow in the evaporator were made such that the, pressure drop for excessive flow would cause the pressureopening valve to close, when the pressure in the liquid container was justat its normal value.

Liquid transfer I When the main evaporator is replaced by an insulated delivery line, a liquid transfer appara containers.

tus results. A pressure of even 5 to 10 p. s. i. sufiices for dispensing liquid rapidly from the pressure container to other containers, at atmospheric pressures. Delivery at -100 p. s. i. is

-practicable with commercial containers, and

pressures of 400 p. s. i. are possible with special Recharging of high pressure converters without blow-down loss is thus possible, when they are used in such a manner that the gas pressure can be reduced to fairly low values by successive equalization of pressure with several of the empty cylinders to be charged.

The pressure built up for forcing the liquid 7 through the delivery line does not involve warming of the delivered liquid; hence, cold liquid of low vapor pressure can be delivered. This eliminates the evaporation which would otherwise permit transfer.

occur in open receiving containers if all of the liquid had to be warmed to generate pressure to It also makes possible the transfer, in closed systems, of sub-cooled liquid of which the vapor pressure is even less than atmospheric.

High pressure equipment of this type may serve in fuel and gas injection in rocket and jet engines,

and for supercharging engines for power bursts.

Electrically heated converters It is clear that the described apparatus can be easily modified to utilize electric power for evaporating and warming the oxygen, if desired. An electric heater of relatively small capacity would serve in the pressure evaporator circuit. A pressure operated switch would be required to cut off the power when not needed, in addition to the pressure-closing valve.

Performance requirements of components The following brief discussion is limited to the salient features of the various components and problems incident to their construction and performance.

(a) Container.The conventional metal Dewar flasks used as laboratory storage containers are 7 satisfactory for use where the pressures are low (under 50 p. s1.) and the conditions of service are not severe. High accelerations, vibrations, and higher pressures require sturdier construction.

l The conventional spherical shape, with pro tecting neck, is simplest to make and is fairly efficient. However, cylindrical shapes may be more suitable for some applications, and a shorter neck may be desirable for compactness.

To gain the advantages of a long conduction path and at the same time obtain compactness, a multiple reentrant neck could be used.

An alternate construction would be to support the inner container by long wires of low heat conductivity, with coiled tubes for access to the cavity. When the access tubes are not used for support, they may be made of corrugated tubing to further increase the heat leak path.

These considerations are not of much im portance for aircraft use, where long storage of liquid in the converters may not be necessary, but are more applicable to storage containers.

(1)) Supporting frames-The provision of adequate support and restraint for the container is of great importance for aircraft use.

The container needs to be protected from blows which might dent or rupture the outer shell, and from shocks which might overstress the inner neck. Also the occupants of the aircraft need to be protected from pieces of the apparatus if it blows up when hit by gunfire.

Gunfire'tests made by the Bureau or Aeronautics have shown that the containers of the type used in the experimental work described, and contemplated for service use, fail when hit centrally by gunfire when under pressure. The usual failure is complete rupture of inner and outer spheres at the equator.

For safety, the container should be strengthened to prevent this failure, or an auxiliary enclosure should be provided to restrain the parts from being blown away. The latter solution has seemed easiest to pursue. A network of small cable, holding top and bottom collars on the container, has been found to prevent large fragments from flying. As these collars may also serve as means for supporting and restraining the container, when fastened to the supporting frame, the, cost of the increased safety in added weight is fairly small.

It probably will be desirable to provide some shock abocrbing suspension or material, such as sponge rubber or felt, between the framework and the container, to minimize jarring.

(c) Liquid connection.-The liquid drain tube is best made of stainless steel, for the same reasons as given above. Thin walled tubing can be used and a considerable length can be coiled inside the evacuated space, so that the added heat leak due to this connection can be made very small.

The geometrical design of this drain tube should be made with the requirements of the contents gage in mind. The pressure-measuring connection of the gage is made just outside the container wall. This connection should be at a level such that the pressure at that point will be the same whether the tube is filled with liquid, as during withdrawal, or filled with gas from the liquid trap or gooseneck outward, as when not in use.

((1) Pressure evaporating coiZ.--This coil 6 should offer relatively low resistance to flow, and should be located so that evaporation occurs at a level below the bottom of the liquid charge.

Since the amount of liquid which is evaporated in this coil is small, a length of only a few feet is sufficient. For a l-liter container, 10 feet 91 %-inch 0. D. tubing has been iound, adequate.

(e) Pressure-closing valve-This valve 9 should offer low resistance to flow when open; should close in a narrow pressure range; then should be nearly leak tight against the pressure differential due to the head of liquid in the container. For ease of construction, all the experimental models used have been made with one side of the pressure actuated bellows open to the atmosphere. Thus the valve opens when the gage pressure in the container falls below the set value. Equal- 13' Well, the valves could be constructed with sealed bellows, to maintain a constant absolute pressure in the container. The gage pressure would then vary with altitude. Since the operation of lowpressure o ygen regulators (e. g. those designed for supply pressures of 10-15 p. s. i. gage) is dependent on gage rather than on absolute pressures, the maintenance of nearly constant gage pressure is desirable in supplying these regulators. A deviation of 5 or 10 p, s. i. in the gage pressure might seriously affect their performance. With regulators operating on pressures of p. s. i. or higher, a variation of 5-10 p. s. i. is not apt to be critical, and there is no basis for choice between constant gage or constant absolute supply pressures.

The schematic diagram of Fig. 3 illustrates the construction of the adjustable pressure-closing valve .5 which has been found to have acceptable characteristics. The valve head 53 is attached b stem 54 to the bellows 55 backed by spring 56, the pressure of which may be adjusted by adjusting screw 51 which is locked in place by lock nut 58. The adjusting screw extends through the valve chamber head 53 on which the bellows 55 is mounted. The inside of the bellows may be sealed forconstant absolute pressure delivery or may be open to atmosphere, as by a vent 60, for pressure relative to atmosphere or constant gage pressure, Similar valves have, been constructed in which a manual-closing override is integrally provided.

(1) Pressure-opening vaZve.-The pressureopening valve l5 used in some arrangements operates on the same principle as the pressureclosing valve 9, but the valve opens instead of closing as the bellows is compressed. The construction therefore is quite similar. The initial adjustment should be such that this valve will not open until the pressureeclosing valve has definitely closed, and that it will close on decreasing pressures before the other one opens.

(g) Loaded cheek valoe.-The purpose of this valve 24, as used in the arrangement shown in Fig. 2, for example, is to prevent circulation and further pressure build-up when the pressure is already above the desired value, that is, when the pressure-opening valve I5 is open. To do this, it must be nearly leak tight against the differential pressure due to the head of liquid. A circular metal disk, held by a coil compression spring on a circular ridged seat, gives an adequate seal. The flow capacity is not critical, but it should pass l. p. m. on a pressure drop of not more than one or two p. s. i. This performance can be obtained easily.

(it) Main ecapomtor.-For convenience in design and fabrication, the evaporators 6, l4 and '28 so far used have been made of plain tubing. Finned tubing would probably be advantageous in some applications. Hardened aluminum alloy,

, that the mercury may freeze.

/8 inch 0. D., has been used in the converter. This alloy is sumciently hard that the coil serves as a rugged protecting shield for the container. The factors influencing the design of the evaporator are: the desired maximum continuous evaporation rate, the allowable pressure drop, and the mechanical considerations of size, ruggedness, and appearance. Formation of frost on coils must be taken into account, but with a spacing of hall an inch or more between coils, frosting does not seem to be a major problem.

Using 80 feet of the inch 0. D. tubing, it was found possible to evaporate 200 l. p. m. continuously with a delivery temperature only 2 C. below ambient. In one test, 200 l. p. m. were evaporated for 15 minutes in humid summer weather, to form a good frost layer; then the apparatus was placed in an altitude chamber, and evaporation at 100 l. p. m. (s. t. p.) continued at a simulated altitude of 40,000 feet and at a chamber temperature of 35 C. The delivery temperature was 3 or 4 0. below ambient under these conditions. The frost which formed in these tests was very fragile, like snow, and the outer layers would often fall off. It is believed desirable that the tubing be blackened to promote radiation absorption. This can be done by dyeing while anodizing the aluminum.

(i) Relief valve.--Since excessive pressures may occur, due to long standing, leakage through the pressure-closing valve in the build-up circuit, or excessive heat leak because of structural failures, provision is required for venting gas to reduce or limit the pressure. A conventional spring-loaded relief valve 3 is suitable for this purpose. Special requirements are that the leakage should be negligible at normal operating pressures, even after the pressure has previously been large enough to open the relief valve; the relief-flow capacity should be large enough to balance any heat leak apt to occur; To provide adequate emergency relief, a frangible disc may also be found desirable. The relief valve exhaust port should be so located that frost will not be formed where it can subsequently cause corrosion or freezing of the valve. The valve itself can be located so that the escaping gas under normal operation (venting just enough to balance normal heat leak) is warmed to ambient temperatures before reaching the valve.

(1') Contents gaga-As outlined earlier, the features of a suitable gage [3 for indicating liquid content are merely that it respond to differential pressures which are proportional to the depth and density of the liquid, and that its case withstand pressures greater than the rated operating pressure.

A mercury manometer of glass or plastic is simple to design and is quite satisfactory except This would occur only when the ambient temperature was -40 C. or lower, however, since the liquid oxygen is far removed from the gage and has no cooling effect on it.

Various other obvious modifications in the construction and arrangement of parts of the apparatus described may be made without departing from the spirit and scope of this invention, as defined in the appended claims.

This application is a division of my co-pending application Serial No. 645,692, filed February 5,

10 1946; now Patent No. 2,576,985, December 4, 1951.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. Liquid-gas converter apparatus comprising an insulated container having lower and upper sections, a pressure build-up circuit having an evaporating and warming coil between the lower and upper sections of the container, a supply circuit having an evaporating and warming coil connected to the lower section, and a liquid trap device connected in the pressure build-up circuit between the evaporating and warming coil and the lower section of the container, said coils being combined as a single coil unit common to both circuits.

2. The liquid-oxygen converter apparatus as defined in claim 1 including additionally a pressure actuated cut-off valve connected between the upper section of said container and the upper end of the common coil unit to complete the pressure build-up circuit, and an economizing circuit having a pressure-opening valve actuated at a pressure above that of the pressure actuated cutoff valve, connected between the upper container section and the outlet of the supply circuit.

3. Liquid oxygen converter apparatus comprising an insulated container having upper and lower sections, pressure build-up and supply circuits having a common evaporating and warming coil substantially below the normal level of the liquid in said container, a liquid trap interposed between said coil and the lower section of said container, a cut-off valve connected between the upper section of said container and the upper end of said coil to complete the pressure build-up circuit, and a delivery outlet connected between said cut-off valve and coil to complete the supply circuit.

4. Liquid oxygen converter apparatus as defined in claim 3, said cut-off valve being pressure operated, and a manual valve connected in series with said pressure operated cut-off valve between the upper container section and upper coil end to control operation of the cut-off valve.

5. The liquid oxygen converter apparatus as defined in claim 3, including additionally an economizing circuit connected between the upper section of said container and said delivery outlet in parallel to said cut-off valve, said economizing circuit including a valve.

6. The liquid oxygen converter apparatus as defined in claim 5, said cut-off valve being pressure actuated to close, and said economizing circuit valve being pressure actuated to open at a pressure above that of cut-off valve actuation, and a manual valve connected in series with the cut-01f valve between the upper container section and the upper coil end.

WILLIAM A. WILDHACK.

References Cited in the file of this patent UNITED STATES PATENTS Number 

